1. Field of the Invention
This invention relates to processes in which mild thermal cracking takes place in the presence of both steam and an added material and especially relates to such processes in which ammonia is added. It specifically relates to processes in which sulfur and deleterious metals are removed through a phase separation achieved by the injection of brine.
2. Description of the Prior Art
Visbreaking or viscosity-breaking is the name of an old thermal process for reducing the viscosity of crude oils and generally unsalable residues such as straight-run residuums for the purpose of decomposing the oil just enough to lower its viscosity and pour point so that it can be pumped more easily, without attempting to produce significant amounts of gasoline. It is generally a short-time decomposition which is conducted at low cracking temperatures at the heating-coil outlet, such as 800.degree.-950.degree. F. (443.degree.-510.degree. C.), so that liquid-phase cracking takes place at these low-severity conditions. In addition to the major product, fuel oil, material in the gas oil and the gasoline boiling range is produced. The gas oil may be used as additional feed for catalytic cracking units or as a heating oil.
U.S. Pat. No. 1,956,567 describes a watercycle aquolyzation process for visbreaking a heavy petroleum oil of the gas oil type with a large excess of water, such as 3:1 to 5:1 parts by weight of water:oil, at temperatures of 900.degree.-1300.degree. F. (482.degree.-704.degree. C.) and at pressures of 3,000-3,500 pounds per square inch to convert from one-half to three-fourths or more of the heavy oil to liquid hydrocarbons boiling below 430.degree. F. or 450.degree. F. (221.degree. C. or 232.degree. C.). The addition of ammonia or a mixture of ammonia and water is suggested for some stocks, catalytic material being additionally added to form amines or similar compounds that are useful in reducing engine knock. It also suggests that combination of ammonia with the components of the gas oil can be facilitated as desired by modifying temperatures and pressures.
U.S. Pat. No. 2,972,577 shows that a small quantity of pyridine added to Mara Western Venezuela crude before distillation causes substantially all of its vanadium content to be isolated in the distillation residue, apparently by rapidly forming a non-volatile pyridine-vanadium complex.
U.S. Pat. No. 3,132,085 teaches reducing the formation of heat-insulating, carbonaceous deposits on heat transfer surfaces that are contacted with thermally unstable hydrocarbon oils, such as alkylate gasoline or furnace oils, at temperatures of about 350.degree. F. or more. Such reduction of deposits is obtained by adding a condensation product formed by condensing ammonium hydroxide, formaldehyde, and a monoalkylphenol having 4-12 carbon atoms in the alkyl substituent.
U.S. Pat. No. 3,293,314 discloses the use of ammonia to reduce coke lay-down on acidic oxide catalysts used for isomerization of alkyl aromatic hydrocarbons.
U.S. Pat. No. 3,380,909 discloses that an antifoulant additive to hydrocarbon streams, before liquid and/or vapor phase refinery processing, can substantially reduce the fouling of heat-exchanger surfaces. This anti-foulant is obtained by reacting a polyalkylene amine with urea.
U.S. Pat. No. 3,773,651 discloses that in order to neutralize acidic components of curde oil it is general practice to introduce ammonia, morpholine or other basic reagents into the crude column overhead vapor line.
U.S. Pat. No. 3,819,328 describes the use of polyamines to control acid corrosion in petroleum distillation columns and compares them with ammonia and morpholine.
U.S. Pat. No. 4,062,764 discloses amines for neutralizing acidic components in the condensate obtained from distilling petroleum products and points out problems associated with the use of ammonia or morpholine.
U.S. Pat. No. 3,948,759 describes a visbreaking process for heavy hydrocarbon feed stocks, such as atmospheric and vacuum residua, heavy crude oils, and the like, to produce predominantly liquid hydrocarbon products of the motor fuel range, fuel oils, and lubricant base stocks by contacting these feed stocks in the presence of hydrogen with a regenerable alkali metal carbonate molten medium containing a glass-forming oxide, such as boron oxide, at a temperature up to about 1000.degree. F. (538.degree. C.) and at elevated pressures. It specifically teaches that metals can be deposited in the molten carbonates by cleavage of metalloporphyrins.
Various hydrocarbon charge stocks such as crude petroleum oils, topped crudes, heavy vacuum gas oils, shale oils, oils from tar sands, and other heavy hydrocarbon fractions such as residual fractions and distillates contain varying amounts of non-metallic and metallic impurities. Charge stocks derived from Mid-Continent, Louisiana, and East Texas crudes contain small amounts of metals. For example, some East Texas crudes contain about 0.1 part per million of vanadium and 2-4 parts per million of nickel. Charge stocks derived from West Texas crudes and foreign crudes, however, can contain larger amounts of metal. Kuwait crude can contain over 32 parts per million of vanadium and over 9 parts per million of nickel while Venezuelan crudes can contain 200-400 parts per million of vanadium and 17 to 59 parts per million of nickel.
The non-metallic impurities include nitrogen, sulfur, and oxygen and these exist in the form of various compounds and are often in relatively large quantities. The most common metallic impurities include iron, nickel, and vanadium. However, other metallic impurities including copper, zinc, and sodium are often found in various hydrocarbon charge stocks and in widely varying amounts. The metallic impurities may occur in several different forms as metal oxides or sulfides which are easily removed by single processing techniques such as by filtration or by water washing. However, the metal contaminants also occur in the form of relatively thermally stable organo-metallic complexes such as metal porphyrins and derivatives thereof along with complexes which are not completely identifiable and which are not so readily removed.
Such thermally stable organo-metallic complexes are high-boiling molecular structures that make up the residual portion of a crude oil, e.g., nickel or vanadium bound in a porphyrin structure. Hence, processing of residuas from certain fields is particularly hampered by their heavy metals content.
The presence of the metallic impurities in the hydrocarbon charge stocks causes much difficulty in processing of the charge stocks. The processing of the charge stock, whether the process is desulfurizing, cracking, reforming, isomerizing, or otherwise, is usually carried out in the presence of a catalyst and the metallic impurities tend to foul and inactivate the catalyst to an extent that may not be reversible. Fouling and inactivation of the catalyst are particularly undesirable where the catalyst is relatively expensive, as, for example, where the active component of the catalyst is platinum. Regardless of the cost of the catalyst, fouling and inactivation add to the cost of the processing of the charge stock and therefore are desirably minimized.
Thermal processing of the hydrocarbon charge stock can remove a portion of the metals. However, thermal processing results in conversion of an appreciable portion of the charge stock to coke, thus causing a loss of charge stock that desirably should be converted to a more economically valuable product or products. Moreover, by thermal processing, the metallic impurities tend to deposit in the coke with the result that the coke is less economically desirable than it would be in the absence of the metals.
Metals can also be removed by catalytic hydroprocessing of the charge stock. However, catalytic hydroprocessing results in the catalyst becoming fouled and inactivated by deposition of the metals on the catalyst. There is no convenient way of regenerating the catalyst and it ultimately must be discarded. Since these catalysts are relatively expensive, catalytic hydroprocessing to demetalize hydrocarbon charge stocks has not been economically practicable.
There is, consequently, a need for a process that will adequately reduce the molecular weight of a heavy crude and simultaneously remove metals therefrom, such as by splitting large hydrocarbon molecules and the metalloporphyrins combined therewith, in order to provide a wide variety of readily utilizable refinery charge stocks.
The present invention is mainly focused on cleavage of these complexes and removal of the metals while visbreaking and creating minimal coke formation.